Being new on the job is tough enough without adding mistakes – be sure to check your work and don’t do any of these 10 Rookie mistakes!
1. Forgetting to save configurations before a reboot
2. Not sending out notifications regarding planned outages
3. Putting a new switch into an L2 net that uses VTP without resetting the VTP config revision and corrupting or clearing VTP DB
4. Not checking the vtp sequence number
5. Changing the interface ip on a router before adding routes to new subnet via telnet to really remote site
6. Not cross referencing the documentation where applicable and updating the documentation if incorrect
7. Not adding reload in XX mins before making a change which locks you out of your device
8. Simply forgetting the keyword "add" in the command in manipulating allowed VLANs across a trunk link - which resulted in the existing allowed VLANs being replaced by the singular VLAN, "switchport trunk allowed vlan ADD <vlan ID>""
9. Not asking -- if you are unsure about implementing something ask !
10. Lacking humility or thinking we have all the answers
If you have any others to add please leave them below; best of luck!